A. Field of the Invention
The present invention relates generally to a disk antenna, and more particularly to a disk antenna for use in spread spectrum and discrete frequency applications, such as a Wide-Local-Area-Networks (WLANs), portable computers, handheld data collection devices, and wearable communications devices.
B. Description of the Prior Art
With the advent of network communications systems and portable computing and communication devices, the market interest has turned toward wireless networks in which users are provided with the benefits of network computing without drawbacks of being physically connected to the network, thereby allowing for portable network devices. In meeting the demand for wireless network services, developers are faced with multiple problems. Crowding of radio frequency spectrum and government regulations limit the amount of spectrum available for such services. Currently in the U.S., the ISM (Industrial, Scientific and Medical) radio frequency spectrum in the 2.4-2.5 Giga-Hertz (Ghz) range provides an unregulated region in which wireless network development has occurred free from government regulations. As may be expected this spectrum is widely used by a variety of digital and analog communication systems resulting in a substantial amount of radio frequency noise. While analog voice systems are forgiving of such noise, digital communication systems are more sensitive to noisy operating environments.
Recently, the commercial development of communications systems using spread-spectrum techniques has provided a way for wireless communication to provide digital signals with a reliable communication link even when operating under radio interference noise within the desired radio frequency spectrum. However, spread spectrum systems in order to operate for their intended purpose require a communication bandwidth that is greater than the bandwidth of the transmitted signal. This allows for the transmitted signal to be spread across the communication bandwidth in way that isolates and distinguishes the transmitted signal from the radio interference noise.
In the past, the development of these system has focused primarily on the transceiver devices and digital modems for conveying the transmitted signal using the spread spectrum technique. However, as the demand for wireless networking applications have grown, the desire to implement these system in smaller and more portable devices have grown.
Transmission of the signal ultimately requires some type of antenna to resonate or receive the signal from the electromagnetic energy that makes up the radio spectrum. In portable-wireless network applications, it is also desirable that the antenna be unobtrusive so as to not detract from the aesthetic and functional designs of the systems which implement a wireless communication application.
Such antennas must be able to operate in applications where the position of the antenna is changing, thus the antenna must be able to transceive omni-directionally thereby allowing the user flexibility to move about while maintaining a connection with the digital network.
Applications for such antennas may require that the antenna be mounted internally within a portable device or contained within a computer cartridge, such as the PCMCIA card type cartridges which make up the current standard for portable and laptop computers.
Providing an antenna in such small environments such as a computer cartridge presents certain problems when scaling down the antenna dimensions. For example, the space allocated for the antenna may be only a fraction of the cartridge space which also accommodate the digital modem and transceiver equipment. This space limitation limits the size of the radiating element that makes up antenna which in turn limits the bandwidth or radio frequency range in which the antenna is useful. As indicated above, it is desirable to maintain a large communication bandwidth for spread spectrum techniques. Furthermore, limiting the size of the radiating element can cause the antenna to be more sensitive to radio frequency interference from the nearby environment such as the transceiver and digital modem components. The noise can cause the resonate frequency of the antenna to shift thereby causing the operating bandwidth of the antenna to shift out of its desired operating range. Because smaller sized antennas are already provided with a smaller bandwidth, such shifts can severely limit the useful radio frequency range available. Thus, need exists for a compensating means to tune or adjust the antenna to compensate for the RF interference from the operating environment.
A conventional antenna of the type suitable for small compact operating environments is the disk type antenna. However, disk antennas currently manufactured to meet the space requirements demanded by computer cartridge vendors are limited in operational bandwidth, thereby limiting the benefits from spread spectrum techniques. The limited bandwidth also serves to amplify the effect of RF interference which shifts the resonant frequency. Presently, application specific tuning of disk antennas is not practicable as it requires retooling of the manufacturing process. Thus, antenna manufactures have imposed strict environmental requirements on the orientation of the antenna in relation to other electronic components in the computer cartridge. Such requirements, while minimizing environmental RF interference, place restrictions on the designers of wireless networking cards. Such a trade-off often causes the designer to sacrifice antenna performance for other considerations. Thus, it is desirable to provide a disk antenna having a small footprint for computer cartridge applications, while maximizing bandwidth and compensating for noise caused by the operating environment.